It is widely known that the construction of oil pipelines is an extremely expensive and time consuming operation which is fraught with numerous difficulties. Typically, 40 foot pipe sections having a diameter of about four feet are welded together by hand for example, in the current construction of the Alaskan pipeline. Welding is performed by hand all the way around a v-shaped notch between the pipe sections and each weld typically takes 12 man hours of direct labor. Relatively elaborate equipment is also necessary to properly align these pipe sections during this hand welding process. Obtaining labor for this purpose, particularly in the upper Arctic regions, is difficult and is very expensive due to the necessary inducement required to obtain the work forces. Also due to the very time consuming process of hand welding, labor costs are enormous. For example, it is recently estimated that the cost of the 800 mile Alaskan pipeline will be in the neighborhood of 6 billion dollars, most of which is reflected in labor costs and capital expenses relating to expensive machinery which is tied up for long periods of time on the job. It is estimated that the pipeline material cost is merely 300 million dollars out of the above-mentioned 6 billion dollar figure. Thus, it is highly desirable to sharply reduce labor costs and the tying up of expensive equipment. Furthermore, due to the inclement weather in Arctic regions, special houses are often lowered by crane over the working areas since such inclement weather interferes with the welding process.
It is thus highly desirable to sharply reduce labor costs and reduce the use of very time consuming alignment procedures in the construction of oil pipelines. Also, it is highly desirable to reduce the overall construction time. However, at the same time, it is necessary to produce very high quality welds to prevent oil spills which could result in large losses of oil and could contaminate the environment. In grappling with these problems, I became aware of the use of "Thermite" welding, taught in the prior art. For example, U.S. Pat. No. 1,355,224 to Gravell, teaches the positioning of a "Thermite" pellet between two thin sheets of metal. Upon the analysis of this technique, it became apparent to me that this technique could not be applicable to the welding of pipelines because the interface between the sheets becomes contaminated with the products of the "Thermite" reaction, and hence the above-mentioned high quality welds could not be effected through the use of this teaching. This patent also teaches the employment of pressure between the sheets to maintain contact, which teaching would not be desirable in the pipeline problem. Gravell also teaches at the bottom of Column 3 that "Thermite" tablets may be placed outside of one or both of the sheets to be joined. This teaching is also useless in connection with the solution of the pipeline problem because a majority portion of the heat generated on the coupler exterior would not penetrate the pipe coupler to the interface to be welded and would be lost to the outside environment. Additionally, placing "Thermite" bodies on the outside of pipes would produce a safety hazzard. In summary, the teachings of Gravell would be useless for my purposes.
U.S. Pat. No. 3,308,532 to Long et al., teaches the use of an annular exothermic body for generating sufficient heat to activate an annular body of brazing material. Brazing, which is related to soldering, produces low strength joints with, by definition, a non-ferrous filler material. The base material, steel pipe in this case, cannot be made hot enough to melt, not even very local to the joint. Therefore, the brazing alloy must be a metal that melts at a much lower temperature than the base material.
Steel melts at about 2,700.degree.F. Typical brazing alloys melt anywhere from 1,100.degree.F to 1,900.degree.F. Thus, even a relatively high temperature braze can be applied at about 800.degree.F below the melting point of steel.
Despite their relatively low strength, brazed joints are often used instead of welds because they are so much easier to apply. They require lower temperature, and less fine temperature control since a braze can be overheated by several hundred degrees without anywhere melting the steel parts being joined. Brazed or soldered joints are thus commonly used in non-critical applications.
Though Long uses an exothermic chemical heat source, his process is nevertheless a braze and so the performance he requires from the reaction is minimal. He desires to generate a minimum amount of heat, which would be sufficient to activate the brazing material but which could not possibly affect true welding, i.e., melting of the interfaces. He states in Column 3, lines 25-35, that the base metals will not undergo physical or metallurgical damage during the exothermic reaction which implies that he is not even using a high temperature braze but rather is operating entirely below about 1,400.degree.F, the temperature at which steel undergoes crystal phase change. It is obvious that true welding of steel pipe cannot be produced by the teachings of Long, and that his process is inappropriate for any application where high joint performance is critical.
Aside from the above, there has also been some development of "Thermite" welding techniques in the public domain over the years. These developments have involved use of a separate refractory vessel, often graphite, in which "Thermite is reacted. Molten reaction products are then poured from the vessel as required, after the reaction is completed, for use as a source of heat and/or filler material.
"Thermite" iron is typically used as filler material in producing large, low performance welds. It is difficult to prevent or control the occurrence of impurities in "Thermite"-generated iron, which prevents its use as a high-quality weld material.
Molten "Thermite" iron is used as a source of heat only in some applications. The parts to be welded are generally pressed very tightly together and preheated, as with an oxyacetylene torch. Final heating, with reacted "Thermite" poured over the joint, forms a weld. The process is elaborate and requires extensive preheating, because the "Thermite" is reacted in a separate vessel.